After police dashcam video of the 2014 shooting of a 17-year-old African American went viral, Chicagoans began to ask why there was no audio on any of the footage.

A new investigation claims that up to 80 percent of CPD dashcam video is silent and attributes the absence of sound mostly to officers tampering with the recording systems.

DNA Info Chicago recently reported the results of a survey of dashcam video stored by Chicago Police Department technicians and found the bulk of them lacking audio. Some 1,800 police maintenance logs were also reviewed, revealing many squad cars going months without repairs to the systems. Further, maintenance personnel reported much of the damage to the systems was likely done on purpose by the officers themselves while in the field.

“Chicago Police Department officers stashed microphones in their squad car glove boxes,” the news site reported. “They pulled out batteries. Microphone antennas got busted or went missing. And sometimes, dashcam systems didn’t have any microphones at all.”

In the case of the now-infamous shooting of Laquan McDonald, fully four of the squad cars on the scene during the incident had no audio recorded accompanying video of the shooting, including the car that took the famous video as well as the car driven by the officer who shot the teen 17 times.

Indeed, the car assigned to Jason Van Dyke, the officer seen on video killing the teenager, and his partner, Joseph Walsh, is typical of the constant destruction of the audio capabilities of the dashcam system.

The audio system of Van Dyke’s car number 6412 had been reported broken earlier in the year before the teen was shot in October of 2014. And even though it was fixed after a three-month wait, only a day later it was reported broken all over again. Maintenance operators wrote in their log that the system had seen “intentional damage” in the field.

Several of the other CPD vehicles on the scene of the McDonald shooting had similar audio problems and causes noted in the maintenance logs.

A January 30 article in The Washington Post reported that Chicago’s is not the only big city police force with officers purposefully damaging the audio capabilities of dashcam systems. Los Angeles has also had its share of dashcam tampering by officers.

Since the release of the McDonald video, the Chicago Police Department has been accused of a “culture of cover-up,” leading to the quashing of a string of police dashcam videos allegedly proving officer misconduct. The New York Times speculated that Mayor Rahm Emanuel kept the McDonald video out of public view until after he won a tough re-election battle.

This attempt to keep such videos under wraps had sparked months of street protests in Chicago. The trouble with the dashcam videos also led to the firing of an investigator of the city’s Independent Police Review Authority after he refused to agree that one CPD shooting video was a justified shooting.

The release of the McDonald video, said the attorney of another man killed by CPD, was a “perfect storm of exposure,” revealing the corruption. “It was very difficult given the timing of things for our leaders to deny that there was a coverup,” the attorney added.

Meanwhile, 23 Chicago Police officers have been called before a federal grand jury tasked with trying to determine if the department is responsible for violating Laquan McDonald’s civil rights.

Follow Warner Todd Huston on Twitter @warnerthuston or email the author at igcolonel@hotmail.com